In recent years, a robot is used in various working sites, and the smoothness and high speed of its operation are important.
A conventional apparatus for generating a trajectory for an industrial robot will be described below. A trajectory along which a robot passes to carry out a specified operation is determined in such a manner that an operator registers, in advance, a plurality of teaching points through which the robot must pass, and passing points between the teaching points are interpolated with straight lines, arcs or parabolas. In teaching point data that gives information on the teaching points, the position of a teaching point, the coordinates of an attitude, a speed at which the robot passes between the teaching points, and the like are specified. In the case where the robot is moved in a simple straight-line motion from one teaching point to a next teaching point, a straight line trajectory connecting the teaching points is obtained by interpolation arithmetic between the teaching points. In the case where the robot is moved in straight lines among three teaching points, when a bent angle of a polygonal line is large, the speed of a tip portion is largely changed at the node of the polygonal line, so that leading-edge oscillation is caused to occur. Also, since a large acceleration is applied to a joint axis of the robot when the tip portion passes through the bent point of the node of the polygonal line, the components of the robot, such as a reduction gear, are caused to bring shortening of lifetime, its destruction or the like.
In order to overcome these problems, Japanese Patent Publication No. 1-27443 or Japanese Patent Application Laid-Open No. 4-111006 discloses to provide means for generating a trajectory turning the inside of a node by connecting two lines constituting the polygonal line by a smooth curved line without passing through the bent point. Also, there is proposed a method of generating a trajectory for a robot in which the change of an angle of respective axes at a teaching point is made smooth, the operation time is shortened, and the error of a path at the teaching point is suppressed within a predetermined allowable error of a path.
However, even by the above means for operating the robot along the trajectory turning the inside of the bent point of the polygonal line, since moving speed is determined for every interpolated interval put between the teaching points, if the specified speeds are different between intervals before and behind a teaching point, discontinuous change of speed occurs so that oscillation is caused.
Also, according to an object of protecting mechanical parts of a robot or the contents of an operation to be carried out by a robot, there is a case where an acceleration value occurring at the operation is restricted. In this case, there is a possibility that the moving speed of a tool tip of a robot registered in the teaching point data can not be faithfully realized, so that it is required for an operator to set the speed again.